An overview is presented of the principal features of the El
Niño-Southern Oscillation (ENSO) teleconnections in terms of regional
patterns of surface temperature, precipitation and mid-tropospheric atmospheric
circulation. The discussion is cast in the context of variations in the
associations over time, with decadal scale changes emphasized. In the five
decades or so for which we have adequate records to reliably analyse the global
aspects of ENSO effects on regional climates around the world, we have
witnessed one major decadal scale change in the overall pattern of sea-surface
temperatures (SST) in the global ocean, and concomitant changes in the
atmospheric response to those changes. The analysis underscores the connection
between low frequency changes in tropical SST, ENSO and decadal scale changes
in the general atmospheric circulation, pointing to the complex interplay
between the canonical ENSO system, slow changes in SST in the Indo-Pacific over
the last century, and long-term changes in the atmospheric circulation itself.